Because of widely recognized fuel economy and performance advantages, fuel injectors are enjoying expanded use in internal combustion engines. In most instances, however, the manufacture of fuel injectors has involved a compromise between manufacturing cost and desired performance capabilities. In some cases, it has been necessary to sacrifice simplicity to achieve necessary or desired performance goals. For example, U.S. Pat. No. 2,350,434 (to Wallgren et al) discloses a fuel plunger pump combined with an injector nozzle wherein by virtue of rotatable sleeves, the effective length of the pump stroke may be varied to accommodate changing operational conditions. However, this desired performance requires a complicated design including a series of interconnected recesses, bores and passages in and through the plunger, the multiple sleeves and the multipart casing.
U.S. Pat. No. 4,280,659 to Gaal et al discloses a fuel injector assembly designed to achieve improved operation including an injector body, a barrel, and a cup positioned in an end-to-end relation wherein special precautions are required to avoid fuel leakage from the machined interfaces between, for example, the injector cup and the barrel. Despite expensive, high tolerance machining of the components forming the assembly, Gaal et al require that an additional annular groove be formed between the cup and the barrel to control fuel seepage, further complicating the structure and the manufacturing process thereof.
U.S. Pat. No. 4,410,138 to Peters et al (assigned to Cummins Engine Company, Inc.) attempts to solve the problem of complexity in fuel injector assemblies by eliminating axial fuel passages from the two piece injector body. However, the disclosed design will require the body to be formed in two parts which must be subsequently joined. The injector plunger is also formed with an internal flow passage for scavenging fuel flow which further increases the cost and complexity of this design.
A second patent to Peters (U.S. Pat. No. 4,441,654 also assigned to Cummins Engine Company, Inc.) discloses another attempt to form a simplified fuel injector but again the disclosed design requires a two part body which must be permanently joined together thereby complicating the manufacturing process. Like U.S. Pat. No. 4,410,138, the Peters '654 patent discloses the advantages of reducing or eliminating axial drilling by using only radial passages to connect the central axial bore with the exterior of the injector body to provide flow passages between the fuel supply/drain systems of the engine and the interior of the injector. This design, however, constrains the location of the common fuel supply rail and the fuel drain rail to positions corresponding to locations of the corresponding radial passages contained in the injector body. Such rail locations may not be ideal in a given engine head design.
Attempts to simplify the formation of longitudinal passages in mechanical devices other than fuel injectors are known. For example, U.S. Pat. No. 2,468,824 to Hughey discloses a method for making a tip for a gas torch in which passages are provided by milling longitudinal slots on a central core piece or insert and completing the passages with a long sleeve fitted tightly about the insert. Although suitable for the purposes disclosed, there is no suggestion of how this technique might be employed to simplify the design of a fuel injector without sacrifice of important performance goals for the injector.
While the disclosures and teachings of the above-noted patents evidence some progress, a fuel injector assembly which is simple and inexpensive to manufacture and use has, nevertheless, remained an allusive objective.